The present invention relates generally to overcurrent protection devices and more particularly to a sneak current device for the protection of telecommunication equipment against abnormal current levels.
Equipment protection devices which guard against abnormal current levels are well known in the art. A typical example is a one shot device employing a low melting point material which will melt upon the occurrence of an over-current condition and ground the device. These devices do provide protection but do not provide a short enough response time and are not resettable for small current overloads. The time delay in heating up the melting material is too long for some applications. Also the devices tend to vary one from another because of slight differences in compositions of the melting material which cause for different melting temperatures. In addition if a large variation in ambient temperature range exists in which this device operates, the current level which causes a failure condition can vary appreciably. Other types of devices are resettable for small overcurrent conditions but do not permanently ground the device for large overcurrent conditions.
Accordingly it is an object of the present invention to provide an improved overcurrent protection device.
It is another object of the present invention to provide an overcurrent protection device with improved response time to an overcurrent condition.
It is a further object of the present invention to provide an overcurrent protection device with an ambient temperature compensating feature.
It is still a further object of the present invention to provide an overcurrent protection device which is of simple, inexpensive and rugged construction.
Other objects and features of this invention will be in part apparent and in part pointed out hereinafter.
Briefly, the overcurrent sensing device of this invention comprises a housing member to which a set of line contacts are secured and in which a nonresettable, two-position snap-acting blade and a thermostat metal assembly in cantilever mounted. The line contacts, snap-acting blade, and thermostat metal assembly are electrically insulated from one another but still are stacked in close proximity to each other. The snap-acting blade is electrically connected to ground while the thermostat metal assembly is connected to the line source for transmitting current to the operating equipment. Upon the occurrence of a mild overcurrent condition, the thermostat metal assembly heats up and bends to come into contact with the snap-acting blade and therefore ground the line current. On reoccurrence of a normal current level, the assembly returns to its initial position to allow current to flow to the equipment. However, if the overcurrent condition is of a large enough magnitude and for a long enough duration, the assembly will exert enough force on the blade to cause it to snap and come into contact with the line contacts and thus permanently grounding the device. Once in this mode, the device is not automatically resettable.